Pressure-sensitive adhesive sheets generally each include a sheet member having a release function (hereinafter also referred to as “release liner”) and a pressure-sensitive adhesive layer (composed typically of an acrylic pressure-sensitive adhesive) arranged in contact with the sheet member. Releasing (separation) between the sheet member and the pressure-sensitive adhesive layer is possible.
Exemplary known processes for forming the release liner include a process of curing a release agent, such as a silicone release agent, alone to form the release liner; and a process of applying a coat of a release agent to at least a side of a release liner base (substrate) to be in contact with a pressure-sensitive adhesive layer and curing the applied coat. The former process gives a release liner composed of only a layer cured from the release agent; and the latter process gives a release liner having a multilayer structure including the release agent layer as an outermost layer. On the other hand, there have been used release liners composed of polyethylenes and polypropylenes as release liners that do not require coating as above. As a technique for reducing the release force in such release liners, there has been known a technique of using low-density polyethylenes and linear low-density polyethylenes as release layers (see, for example, Patent Documents 1 and 2).
Incidentally, in some pressure-sensitive adhesive sheets, typically those having adhesive layers on both sides, one of the two adhesive layers is applied to an adherend and the other remains in contact with a release liner to form an assembly, and this assembly is subjected to cutting and processing, and then stored for a certain duration before use. Especially when the adherend is a long member or flexible member such as an automobile weather strip, the assembly may be wound as a roll and stored from the viewpoint of space saving. When a pressure-sensitive adhesive sheet with a release liner is stored in a curved state as mentioned above, the release liner may partially separate from the pressure-sensitive adhesive layer to cause so-called “liner pop-off” (liner lifting), and this in turn causes contaminations of the pressure-sensitive adhesive layer.
A possible candidate for inhibiting the liner pop-off is use of a release liner having an increased release force. In this case, however, the release function decreases though the liner pop-off is improved. Specifically, the liner pop-off inhibition and the release function are tradeoffs with respect to each other. As a technique for inhibiting the liner pop-off, there has been known a technique of using, as a release layer, materials containing polar groups (see, for example, Patent Document 3). A release liner of this type, however, is unsuitable for recycling. Demands are now made to provide release liners excelling in recyclability, because the release liners are wasted after use but such environmental loads should be reduced.    [Patent Document 1] Japanese Examined Patent Application Publication No. S51-20205    [Patent Document 2] Japanese Unexamined Patent Application Publication (JP-A) No. S55-80479    [Patent Document 3] Japanese Patent No. 3179516